Fiber optic gyroscopes (FOGs) have certain advantages over mechanically-based gyroscopes, such as solid-state operation (no moving parts), lighter weight, smaller size, lower power, more rapid turn-on time, and higher reliability. Consequently, FOGs have been proposed for rotation sensing in a wide range of application areas. Interest has been directed at a number of application areas, such as attitude and heading reference systems (AHRS) for use in inertial measurement units (IMU), land-based navigation, and well logging for use in the oil and gas exploration industry. Emphasis is clearly being directed toward the development of closed loop systems with scale factor stabilities of about 100 ppm or better. Open loop technology, however, may still find use in applications where moderate scale factor stabilities are sufficient. One area being explored in land navigation is the development of low cost low-medium accuracy devices for automobile guidance and tracking systems with bias drift of about 0.3°/hour or less, and the scale factor of about 1000 ppm or better, which is the level currently being attained by both closed loop and open loop gyroscope systems.
FOGs, accelerometers and FOG-based inertial navigation systems (INS) form key parts of the integrated sensor systems essential for highly accurate autonomous car performance. For localization, the vehicles can use a combination of the Global Positioning System (GPS) and inertial navigation systems (INS). The accuracy of GPS systems has improved significantly since 2000. However, GPS error can still be large—several meters, even under ideal conditions. The errors grow rapidly when obstacles or terrain occlude the sky, preventing GPS receivers from obtaining signals from a sufficient number of satellites. This is a significant concern in urban areas, where skyscrapers create “urban canyons” in which GPS availability is severely limited. GPS is typically coupled with an INS, which consist of components such as odometers, compasses, gyroscopes, and accelerometers, to continuously calculate position, orientation, and velocity of a vehicle without need for external references. INS are used to improve the accuracy of GPS and to fill in “gaps” such as those caused by urban canyons.